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(22) Manipulating Variables

Manipulating Variables (ksh/bash only)

Text variables

The pattern in the following uses the same wildcards as for filename matching.

${#var}: returns the length of $var in characters
${var%pattern}: removes the shortest suffix of $var patching pattern
${var%%pattern}: removes the longest suffix of $var patching pattern
${var#pattern}: removes the shortest prefix of $var patching pattern
${var##pattern}: removes the longest prefix of $var patching pattern

Numeric variables

$(( integer expression )): The $(( ... )) construction interprets the contents as an arithmetic expression (integer only). Variables are referenced by name without the "$". Most of the arithmetic syntax of the 'C' language is supported, including bit manipulations (*,/,+,-,|,&,<<,>>. Use parentheses for changing precedence).

Examples
datapath=/data/public/project/trials/set1/datafile.dat

filename=${datapath##*/}: filename is set to "datafile.dat" since the longest prefix pattern matching "*/" is the leading directory path (compare basename)
path=${datapath%/*}: path is set to "/data/public/project/trials/set1" since the shortest suffix pattern matching "/*" is the filename in the last directory (compare dirname)
i=$((i+1)): often used in while loops

variable-manipulation.src last modified Feb 11, 2005

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